Retaining Units after Changing Strata and Probabilities

Abstract

Survey samples are often based on primary sampling units selected from initial strata with probabilities pj proportional to initial measures. However, later samples can be better served with new strata and new probabilities, Pj, based on new information. The differences between the initial and new strata and measures may be due to changes either in population distributions or in survey objectives. It is efficient to retain in the new sample the maximum permissible number of initial selections. Procedures are presented first for changing measures within fixed strata, then for strata with changed units. Modifications, improvements and simplifications are also introduced.